Is this school you used to study？ 空白处应填where还是at which，为什么?

空白处在this 和school 之间

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两派敏亏个都可以。
Is this the school where/at which you used to study?
=Is this the school that/尘神which you used to study at?
where=介拿态词+which

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空白处在哪里？话说school前面好像少了个the

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